If you are asking about having both programs separately installed on one system, I don't think there is any issue. Both should run just fine and would be totally independent of each other. Just install TS2010 as you normally would.
I should point out that I don't have TS12 though, so I can't actually say for sure. However, I do have TRS2004, 2006 and 2010 all operating on the same system, and all three work just fine with no issues.
If you were asking about combining the programs into one, then I assume Dave has outlined how to do that in the post above.
Patrick